Conventionally, a connecting device of a construction machine is equipped with a thrust bearing to slide under a large thrust load. For such a thrust bearing, a thrust bearing made of a carburized steel or an induction hardened steel has been used in order to obtain sufficient seizing resistance and abrasion resistance for withstanding a high-bearing stress and low-speed sliding condition and a grease lubricating condition. And, recently, in view of the demand for easy maintenance, in order to extend a lubricating interval of a thrust bearing, a thrust bearing, in which a steel is coated with a superhard thermal spray material excellent in seizing resistance and abrasion resistance comprising WC and self-fluxing alloy, is sometimes put in practical use for such a thrust bearing equipped for a connecting device of a construction machine.
On the contrary, a track roller assembly of a construction machine is equipped with floating seals for the purpose of preventing leakage of a lubricating oil from inside thereof, as well as preventing sand or gravel from entering therein. Thus, in many cases, such a floating seal is made of a hard high-strength high-carbon and high-Cr cast iron which has excellent corrosion resistance and improved seizing resistance and abrasion resistance by crystallizing hard Cr7C3-type carbide in a large content of 30% or more by volume.